Optical transmitting/receiving apparatus

ABSTRACT

An optical transmitting/receiving apparatus capable of suppressing electrical crosstalk and magnetic crosstalk, includes: a laser diode/photo diode (LD/PD) integrated module that terminates a single-core bidirectional optical fiber; a circuit board electrically connected to a lead pin led out of the LD/PD integrated module; and a plastic case that accommodates the circuit board. At least a part of the plastic case abuts against the LD/PD integrated module, and impedance of the plastic case is controlled by mixing a conductive filler into the plastic case.

CROSS-REFERENCE TO RELATED APPLICATION

This is a continuation of co-pending U.S. patent application Ser. No.11/892,652, filed Aug. 24, 2007, which is a continuation ofinternational application PCT/JP2006/303465, filed on Feb. 24, 2006,which claimed the benefit of priority from Japanese Patent ApplicationNo. 2005-051674, filed Feb. 25, 2005, all of which are hereinincorporated by reference in their entireties.

BACKGROUND OF THE INVENTION

The present invention relates to an optical transmitting/receivingapparatus including a laser diode/photo diode (LD/PD) integrated modulehoused therein. Specifically, the present invention relates to anoptical transmitting/receiving apparatus capable of suppressingelectrical crosstalk and magnetic crosstalk.

Owing to a rapid widespread of a fiber to the home (FTTH) technology, itis becoming possible to easily stay connected to the Internet all thetime at general homes. With the widespread of the fiber, an opticalsubscriber terminal apparatus (optical transmitting/receiving apparatus)is becoming downsized and low-priced (low-costed).

Up to now, an apparatus including a laser diode LD that transmits light(optical signal) and a photo diode PD that receives light as separatemodules is in the mainstream, so the optical transmitting/receivingapparatus itself is large in size.

In view of the above, a small-sized LD/PD integrated module thatterminates a single-core bidirectional optical fiber (optical fibercable) is proposed (Patent Document 1). With regard to such asingle-core bidirectional LD/PD module, the LD/PD integrated module isaccommodated in a metal housing obtained by processing a metal plateinto a box shape.

In the meantime, such an LD/PD integrated module has a structure inwhich a CAN package of an LD module and a CAN package of a PD module areelectrically connected to the metal housing owing to an adhesivetechnique such as laser welding and have a common ground.

However, in a case where the LD module is driven at high frequency (LDmodulation), owing to parasitic effects of stray capacitance (Cf) oflead pins and inner structural components of optical devices of the LDand the PD, stray inductance (Lf) of the metal housing portion, and thelike, the ground (GND) of the LD/PD integrated module does not becomeideal.

As a result, an electrical crosstalk path is formed between atransmission side (light emitting side) and a reception side (lightreceiving side) of the integrated module, and a magnetic noise (magneticcrosstalk) generates, with the result that reception sensibilitydeteriorates. FIG. 11 exemplifies a mechanism how such electricalcrosstalk generates.

As a countermeasure against the above, it is considered to stabilize aground potential by accommodating a circuit board mounted with the LD/PDintegrated module in a metal case, fixing the metal housing of the LD/PDintegrated module to the metal case, and allowing the metal housingelectrically contact the metal case.

However, the following problems are pointed out. That is, the metal casemakes the entire optical transmitting/receiving apparatus larger in sizeand is complicated in processing steps and heavyweight, and materialcost of the metal plate increases.

Accordingly, there is proposed an optical transmitting/receivingapparatus in which an LD/PD module is accommodated in a plastic casewhich can be downsized, and is processed easily, lightweight, and low incost.

However, in the case where an LD/PD module is accommodated in a plasticcase, problems concerning electrical crosstalk and magnetic crosstalkcome up again. In other words, the above-mentioned problems come upagain as follows. That is, because there is employed a structure inwhich the LD/PD integrated module including an LD module accommodated ina metal housing and an PD module accommodated in a metal housing isfixed to the plastic case, ground of the LD/PD integrated module doesnot become ideal, an electrical crosstalk path is formed between thetransmitting and receiving sides, and a magnetic noise (magneticcrosstalk) generates, with the result that reception sensibilitydeteriorates.

The following are related arts to the present invention.

[Patent document 1] Japanese Patent Laid-Open Publication No.2000-180671[Patent document 2] Japanese Patent Laid-Open Publication No. 06-138347[Patent document 3] Japanese Patent Laid-Open Publication No.2001-268020

SUMMARY OF THE INVENTION

The present invention has been made in view of the above-mentionedproblems, and it is a technical object of the present invention toprovide an optical transmitting/receiving apparatus still having astructure in which an LD/PD integrated module is accommodated in aplastic case and being capable of suppressing electrical crosstalk andmagnetic crosstalk.

In order to attain the above-mentioned object, (1) an opticaltransmitting/receiving apparatus of the present invention includes: anLD/PD integrated module that terminates a single-core bidirectionaloptical fiber; a circuit board electrically connected to a lead pin ledout of the LD/PD integrated module; and a plastic case whose impedanceis controlled by mixing a conductive filler into the plastic case, thataccommodates the circuit board therein. At least a part of the plasticcase is allowed to abut on the LD/PD integrated module.

As described above, the plastic case obtained by mixing the conductivefiller to a plastic case to control the impedance is allowed to abut onthe LD/PD integrated module, so a resistant component is connected to aninductance component forming an electrical crosstalk path in parallel.Accordingly, dumping effect is imparted to resonance frequency of theinductance component, so the electrical crosstalk and the magneticcrosstalk can be suppressed.

(2) In the above-mentioned optical transmitting/receiving apparatus, theLD/PD integrated module may have a structure including a metal housing.The metal housing is allowed to abut on the plastic case mixed with theconductive filler to maintain a contact state, whereby the dumpingeffect can be further imparted.

(3) Further, a conductive spring member may be provided such that a legportion thereof is engaged with a bottom portion of the plastic case,and a flat plate portion continuously provided to the leg portion biasesthe metal housing toward the bottom portion of the plastic case whilethe flat plate portion is brought into contact to a front surface of themetal housing. Owing to the conductive spring member, an electrical pathto the plastic case of the LD/PD integrated module is reliably secured,and the LD/PD integrated module is reliably fixed.

(4) Further, the flat plate portion of the spring member having aconductivity may be bent toward the front surface of the metal housingin a valley manner so as to have a spring property.

(5) Further, the spring member may be provided with a lead plate so asto be connected to a ground terminal or a power supply terminal of thecircuit board therethrough. Accordingly, in a case where the metalhousing of the LD/PD integrated module have a ground potential, it isreliably grounded to a ground terminal of the circuit board, so theground potential is stabilized. Further, in a case where the metalhousing of the LD/PD integrated module has a power supply potential, thepower supply is virtually grounded, so the potential is stabilized.

(6) For a mode that connects the spring member to the circuit board, thelead plate provided to the spring member is made to be a surface mountdevice type (SMD), with the result that processability can be increased.

(7) Further, in a case where the lead plate provided to the springmember is made to be an insertion mount device type (IMD) and isconnected to the ground terminal or a through hole connected to thepower supply, connection to a ground layer or a power supply layer in acircuit board layer is increased. Thus, further lower impedance can beattained and the potential can be further stabilized.

(8) The optical transmitting/receiving apparatus has a structure inwhich: the optical fiber is led out of an end of the LD/PD integratedmodule; and the plastic case mixed with the conductive filler includes abottom portion and a side wall portion. With regard to the plastic case,a part of the side wall portion corresponding to a portion led out ofthe optical fiber may be formed to be an opening in a front direction,and there may be provided a sleeve mixed with the conductive fillerprotruding from an edge of the opening in a lead-out direction.Accordingly, magnetic crosstalk is suppressed especially in the lead-outportion.

(9) The optical transmitting/receiving apparatus according to the aboveitem (1) has a structure in which the conductive filler is mixed withthe plastic case. Alternatively, there may be used an opticaltransmitting/receiving apparatus in which an LD/PD integrated module iscoated with a plastic material whose impedance is controlled by mixing aconductive filler into the plastic case.

According to the present invention, the circuit board is accommodated inthe plastic case whose impedance is controlled by mixing the conductivefiller into the plastic case, and the LD/PD integrated module is allowedto abut on the plastic case. Accordingly, it is possible to suppresselectrical crosstalk and magnetic crosstalk also in a plastic case thatis downsized, easily processed, lightweight, and low in cost.

Other objects, features, and advantages of the present invention will beillustrated in the drawings and described in the attached scope ofclaims, and will be clear with reference to the following description(embodiments).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view showing an optical transmitting/receivingapparatus according to an embodiment of the present invention.

FIG. 2 is a partially cross-sectional front view showing a procedure ofattaching a spring member.

FIG. 3 is a cross-sectional view showing the opticaltransmitting/receiving apparatus viewed from a side direction.

FIG. 4 is a partially cross-sectional lateral view showing a mountingstructure of an LD/PD integrated module.

FIG. 5 is a lateral view showing the spring member.

FIG. 6 is an explanatory view showing an inner structure of the LD/PDintegrated module.

FIG. 7 is a table representing results of an experimental example.

FIG. 8 is a partially cross-sectional lateral view showing anothermounting structure of the LD/PD integrated module.

FIG. 9 is a graph showing relations between a content rate of aconductive filler, a volume resistivity thereof, and flowability of asynthetic resin.

FIG. 10 is a table representing a relation between improvement effect ofcrosstalk and processability of a case in a case of changing the contentrate of the conductive filler.

FIG. 11 is a diagram showing a generation mechanism of electricalcrosstalk.

FIG. 12 is a diagram showing a suppression mechanism of electricalcrosstalk.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, the present invention will be described in more detailreferring to the accompanying drawings. The drawings illustrate apreferred embodiment of the present invention. However, the presentinvention can be implemented in diverse embodiments, and should not beinterpreted to be limited to the embodiment described in thisspecification. Actually, the embodiment is provided in order tothoroughly and completely disclose this specification and tosufficiently represent the scope of the present invention to a personskilled in the art.

(Structure of Optical Transmitting/Receiving Apparatus)

Referring to FIG. 1 showing an embodiment of the present invention, anoptical transmitting/receiving apparatus 1 has a structure in which acircuit board 2 is mounted with a laser diode/photo diode (LD/PD)integrated module 3, and the circuit board 2 is accommodated in aplastic case 4 having an open upper surface, a side wall portion, and abottom portion.

(Structure of LD/PD Integrated Module)

As shown in FIG. 6, the LD/PD integrated module 3 includes a metalhousing 5, and a ferrule 7 made of a ceramic or the like and mounted toan end portion of a single-core bidirectional optical fiber 6 isinserted to one end surface of the metal housing 5 in a longitudinaldirection thereof. A wavelength division multiplexing filter (WDMfilter) 11 being a prism-shaped wavelength multiplexing anddemultiplexing coupler is provided to a portion in the metal housing 5opposing the ferrule 7, reflects, with respect to a direction orthogonalto an optical axis of the optical fiber 6, received wavelength (e.g.,incident light λ=1.55 μm) from the optical fiber 6 by 90°, and allows aphoto diode module (PD module) 8 to receive the light.

The PD module 8 has a CAN package structure, and a photo diode (PD)component 12 inside the PD module 8 receives a reception light from theWDM filter 11 whose focal length is controlled by a lens 10. The PDcomponent 12 is mounted to a component mounting board 13 of the CANpackage alone or in a state where the PD component 12 is in combinationwith an equivalent amplification circuit (TIA: trans-impedanceamplifier). Lead pins 14 for power supply, ground (GND), and output ofelectrical signal are led out of the component mounting board 13, tipsof the lead pins 14 are soldered to lands 9 of the circuit board 2,respectively, and optoelectrically converted electrical signal is outputto the circuit board 2.

Meanwhile, a laser diode module (LD module) 15 is disposed to theoptical axis of the WDM filter 11 opposite to the ferrule. Lead pins 14for power supply, GND, and the electrical signal are led out of the LDmodule 15, tips of the lead pins 14 are soldered to lands 9 of thecircuit board 2, respectively, the circuit board 2 modulates current ofthe LD component 16 to perform electrooptical conversion, and theemission light (e.g., λ=1.3 μm) is emitted from the ferrule 7 to theoptical fiber 6 through a lens 10 and the WDM filter 11.

Further, the metal housing 5 is electrically connected to GND componentsof the lead pins 14 of the CAN package of the PD module 8 and the CANpackage of the LD module 15.

(Structure of Plastic Case)

The plastic case 4 is formed of a polymer-based synthetic resin, forexample, and a conductive filler made of carbon is mixed therewith. Theplastic case 4 mixed with the conductive filler needs to have impedanceof several Ω to several hundreds of Ω in order to exhibit dumping effectwith respect to resonance frequency that the LD/PD integrated module 3itself has, and a material flowability and a case strength of theplastic case 4 need to be considered with regard to fillability to acase mold and processability, respectively.

FIG. 9 shows a relation between a content rate of the conductive fillerand a volume resistivity represented in a first axis, and a relationbetween the content rate of the conductive filler and flowability of thesynthetic resin when mold-processed under a constant pressure and aconstant temperature represented in a second axis. In order to impartimpedance of several Ω to several hundreds of Ω, in the case of theconductive filler made of carbon, it is preferable to add the conductivefiller by approximately 20% to 30%. Further, regarding fillability to acase mold and processability, the material flowability generally fallswithin a range of 1.3 g/min to 6 g/min. Note that the addition amountchanges depending on a processing condition or properties or a length offiber of the conductive filler to be used, and is not limited to theabove.

FIG. 10 represents a relation between improvement effect of crosstalkand processability of the case in a case of changing the content rate ofthe conductive filler. As the addition amount of the conductive fillerincreases, the impedance of the plastic case 4 lowers, but viscosity ofthe material reduces, with the result that processability during moldingdeteriorates. On the other hand, as the conductive filler is added lessin amount, the viscosity of the material increases, with the result thatprocessability during molding is enhanced, but strength for a casecannot be secured, and the impedance of several Ω to several hundreds ofΩ in order to exhibit the dumping effect cannot be imparted.

Further, a glass filler or the like may be further mixed with theplastic case 4 in order to secure the strength for a case in addition tothe conductive filler.

As shown in FIGS. 1 and 3, the plastic case 4 includes a side wallportion 17 provided over four side surfaces and a bottom portion 18 soas to form a accommodating space that is used for accommodating thecircuit board 2. On an inner space side of the side wall portion 17,three claw portions 20 are provided, each of which is formed to be thickdownward. The circuit board 2 is pushed downward from the upper surfaceof the case to the bottom portion 18 thereof, so the circuit board 2 isprevented from falling off and can be fixed thereto.

On the bottom portion 18 of the plastic case 4 corresponding to theLD/PD integrated module 3, a pair of projection claws 21 is formed asshown in FIG. 4, and the LD/PD integrated module 3 is positioned betweenthe pair of projection claws 21. An engagement claw 24 provided to a legportion 23 of a spring member 22 is engaged with each of the pair ofprojection claws 21.

(Structure of Spring Member)

As shown in FIG. 5, the spring member 22 is processed to have a squareC-shaped section having a lower portion open. In the vicinity of a tipend of each of the pair of leg portions 23 vertically bent from a springmain body 25 having a flat plate shape, the inwardly-protrudingengagement claw 24 is provided. Further, in the vicinity of back end ofthe spring main body 25, wing-shaped lead plates (surface mount devicetype: SMD) 26 horizontally protrude in two opposing directions.

The spring main body 25 is bent in a valley manner by a small angle (3to 10° in horizontal direction) in a longitudinal direction of thecenter thereof.

In a case of mounting the spring member 22 to the plastic case 4, asshown in FIG. 2, the spring member 22 is pressed toward the bottomportion 18 from the above such that the engagement claws 24 of the legportions 23 of the spring member 22 are engaged with the protrusionclaws 21 of the plastic case 4, and then the tip ends of the lead plates26 are soldered to the lands (ground terminals) 9 of the circuit board2. In this case, owing to the above-mentioned small-angle processing ofthe spring main body 25 in a valley manner, the LD/PD integrated module3 is reliably fixed to the bottom surface (bottom portion 18) of theplastic case 4, and the metal housing 5 of the LD/PD integrated module 3electrically is brought into contact to the plastic case 4 in a reliablemanner.

In addition, owing to the small-angle processing of the spring main body25 in a valley manner, the electric contact state of the LD/PDintegrated module 3 and the spring member 22 can be maintained reliably,and the LD/PD integrated module 3 is reliably connected to the groundterminal of the circuit board 2 through the lead plates 26 each being aplate spring. Thus, the ground of the LD/PD integrated module 3 isapproximately ideal, and an inductance component of the LD/PD integratedmodule 3 can be reduced.

(Electrical Crosstalk Suppression Mechanism)

FIG. 12 shows a suppression mechanism of electrical crosstalk. Asdescribed above referring to FIG. 11, in the case of driving the LDmodule at high frequency (LD modulation), owing to parasitic effects ofstray capacitance (Cf) of the lead pins and the inner structuralcomponents of the optical devices of the LD and the PD, stray inductance(Lf) of the metal housing portion, and the like, the ground (GND) of theLD/PD integrated module does not become ideal.

As a result, an electrical crosstalk path is formed between atransmission side (light emitting side) and a reception side (lightreceiving side) of the integrated module, and a magnetic noise (magneticcrosstalk) generates, with the result that reception sensibilitydeteriorates.

However, the plastic case obtained by mixing the conductive filler tothe plastic case 4 to control impedance is allowed to abut on the LD/PDintegrated module, so an inductance component (Lc) forming theelectrical crosstalk path is connected to a resistant component (R) inparallel. As a result, the dumping effect is imparted to resonancefrequency of the inductance component, and the electrical crosstalk andthe magnetic crosstalk can be suppressed.

The plastic case 4 mixed with the conductive filler needs to haveimpedance of approximately several Ω to several hundreds of Ω in orderto exhibit the dumping effect with respect to the resonance frequencythat the LD/PD integrated module itself has.

(Explanation on Example)

FIG. 7 shows results of deterioration amounts of crosstalk measured bythe inventors of the present invention in a case where conditionsregarding the combination of the plastic case 4, the spring member 22,and a sleeve 27 are changed. In the figure, there are shown measurementresults of a deterioration amount owing to the crosstalk between a casewhere transmission is not performed by the LD component 16(untransmitted) and a case where transmission is performed(transmitted), while a reception state by the PD component 12 ismaintained.

As apparent from the figure, the plastic cases 4 mixed with theconductive fillers (experimental example numbers 4 to 6) havedeterioration amounts less than those of plastic cases with noconductive filler mixed (experimental example numbers 1 to 3), andexhibit preferable results.

Further, in the case where the metal spring member 22 is mounted andconnected to the bottom portion 18 of the plastic case 4 and the groundterminal of the circuit board 2, the deterioration amount is reduced(experimental example numbers 3, 5, and 6). In addition, comparing theexperimental example number 5 and the experimental example number 6, oneprovided with the sleeve 27 can suppress the magnetic crosstalk in alarge amount.

(Effect of Embodiment)

With regard to the optical transmitting/receiving apparatus 1 accordingto the embodiment of the present invention, first, it is possible forthe LD/PD integrated module 3 to reliably contact the plastic case 4mixed with the conductive filler, and second, it is possible for themetal housing 5 of the LD/PD integrated module 3 to be reliably groundedto the ground terminal of the circuit board 2. Thus, owing to thesynergy effect of the first and second effects, the electrical crosstalkand magnetic crosstalk can be suppressed.

In addition, with regard to the side wall portion 17 of the plastic case4, the side on which the optical fiber 6 is led out of the ferrule 7includes an opening portion. The opening portion is provided with thesleeve 27 for covering the ferrule 7. The sleeve 27 is integrallystructured with the plastic case 4, so the conductive filler is mixedwith the sleeve 27. Thus, owing to the sleeve 27 mixed with theconductive filler, magnetic crosstalk in the vicinity of the ferrule 7can be suppressed.

(Modified Example)

In the above-mentioned embodiment, the description has been made on theLD/PD integrated module 3 by way of the structural example in which thetip ends of the leg portions 23 of the spring member 22 are engaged withthe protrusion claws 21 of the bottom portion 18 of the plastic case 4.However as described above, a structure employing no spring member 22can also suppress electrical crosstalk and magnetic crosstalk as long asthe metal housing 5 of the LD/PD integrated module 3 is disposed so asto contact the plastic case 4. In the case of employing no spring member22 as described above, as shown in FIG. 8, the pair of protrusion claws21 may be caused to protrude upward to approximately a height of theside wall portion 17 from the bottom portion 18 of the plastic case 4 tothereby directly fix the metal housing 5 by the projection claw 21.

Further, the description has been made on the opticaltransmitting/receiving apparatus 1 by way of a so-called pick-tail typestructure in which the optical fiber 6 is directly led out of the LD/PDintegrated module 3 through the ferrule 7. Alternatively, a so-calledresectable structure may be employed in which the optical fiber 6 can bedismounted.

The structure of the optical transmitting/receiving apparatus 1according to the embodiment of the present invention can be modified andstructured as follows.

(1) An optical transmitting/receiving apparatus including: a lightemitting device/light receiving device integrated module being coatedwith a synthetic resin material whose impedance is controlled by mixinga conductive filler, that terminates a single-core bidirectional opticalfiber; a circuit board electrically connected to a conductive terminalled out of the integrated module; and a synthetic resin case thataccommodates the circuit board. In this case, as a coating technique ofthe synthetic resin material, vapor deposition or coating can beemployed.

(2) An optical transmitting/receiving apparatus including: a lightemitting device/light receiving device integrated module that terminatesa single-core bidirectional optical fiber; a circuit board electricallyconnected to a conductive terminal led out of the integrated module; anda synthetic resin case that accommodates the circuit board, in which: atleast a part of the synthetic resin case is brought into contact with onthe integrated module; and impedance of the synthetic resin case iscontrolled by mixing a conductive filler into the synthetic resin case.

Further, with regard to the optical transmitting/receiving apparatus 1according to the embodiment described above, as a mode to connect thespring member to the circuit board, the lead plates provided to thespring member is a surface mount device type (SMD). Alternatively, thelead plate provided to the spring member may be an insertion mountdevice type (IMD).

The present invention can be used to an optical transmitting/receivingtechnology that terminates an optical fiber.

1. An optical apparatus, comprising: an integrated module thataccommodates a laser diode and a photo diode and terminates an opticalfiber; a circuit board electrically connected to a lead pin leading outof the integrated module; and a case that accommodates the circuit boardtherein and that is formed of a material that includes a plasticsubstance; wherein at least a part of the case abuts the integratedmodule; and impedance of the case is controlled by mixing a conductivefiller into the case material.
 2. An optical apparatus according toclaim 1, wherein the integrated module includes a metal housing.
 3. Anoptical apparatus according to claim 2, further comprising: a conductivespring member which is mounted such that a leg portion thereof isengaged with a bottom portion of the case and that a flat plate portionwhich is continuously provided to the leg portion biases the metalhousing toward the bottom portion of the case while the flat plateportion is brought into contact to a front surface of the metal housing.4. An optical apparatus according to claim 3, wherein the flat plateportion is bent toward the front surface of the metal housing in avalley manner and has a spring property.
 5. An optical apparatusaccording to claim 3, wherein the spring member is provided with a leadplate and connected to a ground terminal or a power supply terminal ofthe circuit board through the lead plate.
 6. An optical apparatusaccording to claim 5, wherein the lead plate is connected to the groundterminal or the power supply terminal of the circuit board depending ona surface mount device shape.
 7. An optical apparatus according to claim5, wherein the lead plate is connected to the ground terminal or thepower supply terminal of the circuit board depending on an insertionmount device shape.
 8. An optical apparatus according to claim 1,wherein the optical fiber is led out of an end of the integrated module;the case includes a bottom portion and a side wall portion; a part ofthe side wall portion corresponding to a led out portion of the opticalfiber is formed to be an opening; and a sleeve protruding from an edgeof the opening in a lead-out direction is provided to the case.
 9. Anoptical apparatus, comprising: an integrated module being coated with aplastic material whose impedance is controlled by mixing a conductivefiller, which accommodates a laser diode and a photo diode andterminates an optical fiber; a circuit board electrically connected to alead pin that is led out of the integrated module; and a case thataccommodates the circuit board and that is formed of a material thatincludes a plastic substance.
 10. An optical apparatus, comprising: anintegrated module being coated with a synthetic resin material whoseimpedance is controlled by mixing a conductive filler, whichaccommodates a light emitting device and a light receiving device andterminates a single-core bidirectional optical fiber; a circuit boardelectrically connected to a conductive terminal that is led out of theintegrated module; and a case that accommodates the circuit board andthat is formed of a material that includes a synthetic resin.
 11. Anoptical apparatus, comprising: an integrated module that accommodates alight emitting device and a light receiving device and terminates asingle-core bidirectional optical fiber; a circuit board electricallyconnected to a conductive terminal that is led out of the integratedmodule; and a case that accommodates the circuit board and that isformed of a material that includes a synthetic resin; wherein at least apart of the case is brought into contact with the integrated module; andimpedance of the case is controlled by mixing a conductive filler intothe synthetic resin case.
 12. An optical apparatus according to claim 1,wherein the impedance is controlled owing to a structure in which aresistant component is connected in parallel with an inductancecomponent of an electrical crosstalk path formed between a lightemitting side and a light receiving side of the integrated module.